Causes and effects of autothrottle integrator saturation on the performance of the approach power compensator of the S-3B digital flight data computer

The US Navy´s S-3B Viking, manufactured by the Lockheed Martin Corporation and powered by two General Electric TF34 high-bypass turbofan engines, is a carrier-based, subsonic, high wing jet aircraft, designed for anti-submarine warfare (ASW). The digital flight data computer (DFDC) was designed as a form, fit, and function replacement for the flight data computer (FDC) (CP-1074) portion of the ASW-33 Automatic Flight Control System (AFCS). Control laws and mode logic implemented in the DFDC were designed to provide the stability augmentation, autopilot, and autothrottle functions provided by the FDC, and to correct existing deficiencies with the FDC. Following an extensive simulation and shore-based test program at the Naval Air Systems Command, Patuxent River, MD, shipboard tests of the S-3B DFDC were conducted aboard USS Harry S. Truman (CVN-75) to determine the suitability of the DFDC for shipboard operations. This paper discusses the causes and effects of integrator saturation on the performance of the approach power compensator (APC), or autothrottle, of the DFDC in the S-3B observed during the shipboard tests. APC test methodology and procedures are also briefly discussed.